Biogas: The Energy Revolution’s All-Rounder
Biogas is produced by fermenting biomass. It is a gas containing methane, which serves as a renewable and versatile raw material for generating electricity, heat and fuel, thus vitally contributing to a safe and environmentally compatible energy supply. Biogas can be stored or can be fed into the natural gas grid and is therefore extremely flexible.
Just like natural gas, biogas is a gaseous mixture that is primarily made up of methane. It is produced by microorganisms when they decompose plants, manure or slurry. Biogas is also generated at wastewater treatment plants and waste disposal sites. For use as an energy source, biogas is generally converted into electrical and thermal energy in cogeneration plants (CHP units). The heat generated can be used to heat buildings, for example. Thus, the energy is used twice and in a particularly efficient manner. Electrical and thermal energy produced by biogas plants is especially climate-friendly because the amount of carbon dioxide (CO2) produced during biogas production is more or less equal to the amount absorbed by the energy crops during growth or the amount which escapes as waste decays.
Heat and electricity from one single source of energy
Biogas production also has an indirect impact on climate protection. Here, the controlled fermentation of liquid manure or compostable waste prevents harmful gases such as methane, which contributes significantly more to greenhouse effects than CO2, from escaping. A biogas plant with an installed electricity capacity of about 500 kilowatts (kW) produces about four million kilowatt hours (kWh) of electricity and 4.4 million kWh of heat in one year from about two million cubic metres (m3) of biogas. It therefore replaces the equivalent of 440,000 litres (l) of fuel oil. Thus, a farmer can produce enough electricity for more than 1,000 average four-person households in one year at his power station. At the same time, the CHP unit produces enough thermal energy to heat 150 households.
Biogas producers in Germany can sell the electricity generated for fixed feed-in tariffs in accordance with the German Renewable Energy Sources Act (EEG), which has been in force since 2000. Here, the operator’s share is between 12 and 25 cents per kWh – depending on the size of the plant, the substrate used and the year in which the plant was commissioned. The newer a plant, the lower the compensation for electricity fed into the grid. For example, a new 500 kW plant, connected to the grid from 1 August 2014, only receives about 12.3 ct/kWh.
In 2014, 41,000 people were working in the German biogas industry – in agriculture, plant construction, service, operation and maintenance. Local specialist craftsmen benefit from this.
The basis for biogas generation is mainly agricultural energy crops and farm fertilisers, such as manure or slurry. In 2014, the 7,944 biogas plants in Germany generated about 27,6 billion kWh of electricity, thereby providing about 7.9 million households with environmentally-friendly energy. The biogas plants provide for more than four per cent of Germany’s electricity consumption.
Germany is the largest biogas producer in Europe. However, other countries are also extremely active. The second largest market for biogas plants is Great Britain, which generates electricity predominantly from landfill gas. Italy is in third place. Here, compensation for electricity fed into the grid at a rate of 28 cents per kWh for electricity generated using agricultural raw materials created a real boom up until 2012.
Transporting heat: from the biogas plant to the public district heating system
While the purchase of electricity by the utility companies is statutorily regulated, biogas producers must market thermal energy on their own initiative. It is only seldom that the demand on their own agricultural farms is great enough to use all of the heat produced throughout the year. Instead, heat can, for instance, be fed into a district heating network. In addition to households, especially such consumers who require heat throughout the year, are of interest – for example community buildings such as schools and city halls, retirement homes, swimming pools, greenhouses and fish farms.
Micro gas grids: from the biogas plant to external CHP units
If the heat consumer is very far away from the biogas plant, transporting the heat becomes expensive. In this case, the CHP unit can also be set up at the location which requires the heat. The biogas is simply transported via a pipeline to the satellite CHP unit in the city or at a heat consumer and is then converted into electricity and heat on-site. The waste heat can then be distributed locally at economic rates.
Biomethane in the natural gas grid
After processing, biogas can also be fed directly into the existing natural gas grid. This is because it uses the available infrastructure and is used as a natural gas equivalent (called biomethane). At present, around 150 plants in Germany feed a volume of approximately 600 billion cubic metres (m3) of biomethane into the network every year. The natural gas grid is also fed into in Sweden and the Netherlands.
Biogas as fuel
Biogas, as a substitute for natural gas, can even be used in vehicles. Biomethane is mainly used as fuel in Sweden. The public transport buses in more than ten Swedish cities run on biomethane. The kilometric performance obtained from one hectare (ha) of maize is around 70,000 kilometres (km) – this is equal to one and a half times the circumference of the earth. To date, there are about 180 biogas filling stations in Germany where one can fill up on biomethane as a pure fuel. At least one third of the more than 900 natural gas filling stations mix biomethane with natural gas at ratios of between five and 100 per cent.
Storable energy that can be used at any time
Biogas can be stored without any problems and can thus be used at any time, regardless of the place of origin. This characteristic is capitalised on by combined power plants, for example. They combine different sources of renewable energies in order to supplement their supply and to ensure provision of the required energy volume at all times. Here, biogas plays a significant role due to its storage properties: It compensates for fluctuations in other renewable energies such as wind or solar energy. Because of this potential, biogas is being used more extensively within the context of the approaching transformation of Germany’s energy system.
Contribution to climate protection
The production of biogas makes a significant contribution to climate protection, because methane (a much stronger greenhouse gas than CO2) is used in the biogas plant to ferment slurry (liquid manure) and manure, which otherwise escapes into the atmosphere from the liquid manure tank. However, a biogas plant generates electricity that is virtually CO2 biogas based electricity-neutral from energy crops as well. This means: Only the CO2 emissions from modern biogas plants are less than half.
The third effect is that the fermentation leaves behind a high-quality fertiliser. This digestate is a substitute for mineral fertilisers, which have to be produced using a great deal of energy. This can also help to reduce CO2 thus improving climate protection.
Biogas industry statistics at a glance
Number of plants (of these feeding biomethane)
Increase in power generation capacity in MW per year (including redundant capacity)
Increase in productive power generation capacity in MW (not including redundant capacity)
Installed generation capacity MW (incl. power feed-in through biomethane)
Gross power generation in TWh per year (not including redundant capacity)
Homes supplied with biogas based electricity
CO2 saving using biogasin millions of tonnes
Turnover in Germany in €
*internal extrapolation based on federal state data
**based on expert interviews (as of November 2014)